This Application claims the benefit of Japanese Patent Application Nos. HEI 08-277913 filed Oct. 21, 1996 and HEI 08-298756 filed Nov. 11, 1996, which are hereby incorporated by reference.
1. Field of the Invention
The present invention relates to an exposure apparatus and method for transferring a mask pattern onto a photosensitive substrate, in a photolithography process, used in the manufacture of semiconductor devices, image pickup devices (such as CCD), liquid crystal display devices, thin-film magnetic heads. The invention relates more particularly to a scanning exposure type exposure apparatus and method that operates in a step-and-scan mode.
2. Discussion of the Related Art
In the manufacture of semiconductor devices, a step-and-repeat type (one-time exposure type) reduction projection exposure apparatus (xe2x80x9cstepperxe2x80x9d) has been widely used as an exposure apparatus for transferring a pattern of a reticle as a mask onto each of shot areas of a wafer (or a glass plate) coated with a photo-resist. The industry desires the ability for transference of a large area of a circuit pattern with high accuracy, without increasing the burden on the optical projection system. To accomplish this goal a step-and-scan type projection exposure apparatus has been developed wherein the reticle and the wafer are scanned in synchronization with each other, wherein a part of the pattern on the reticle is projected on the wafer through the optical projection system, so that an image of the pattern on the reticle is sequentially transferred onto each shot area on the wafer.
In a conventional aligner, as a prototype of the scanning exposure apparatus, a pattern of the entire area of the reticle is transferred onto the entire area of the wafer. This provides a non-reverse image at a magnification of 1.0 in a one-time scanning exposure operation using a unit-type stage system.
However, in the step-and-scan type exposure apparatus the optical projection system normally projects an image at a certain reduction ratio or magnification that is smaller than 1.0. Therefore a reticle stage and a wafer stage must be driven independent of each other and at a speed ratio that is dependent upon the reduction ratio of the optical system. Since a stepping mode is employed to position one shot area after another in an exposure region, the driving mechanism of the stage system tends to be complicated and to require highly sophisticated control (refer to Japanese laid-open patent publication No. 7-176468, U.S. Pat. No. 5,646,414 for example).
In the conventional step-and-scan type projection exposure apparatus, therefore, the speed and position of each stage are controlled based on measurement values of laser interferometers, as shown in FIG. 10. Referring to FIG. 10(a1) and (a2), a mirror 52X for measuring displacement along the X-axis and a mirror 52Y for measuring displacement along the Y-axis are fixed on a wafer stage 51 on which a wafer W is mounted. A mirror 55X for measuring displacement along the X-axis and a mirror 55Y for measuring displacement along the Y-axis are fixed on a reticle stage 54 on which a reticle R is mounted. If the rectangular coordinate system of the plane on which the wafer W is moved is defined by the X-axis and Y-axis, and the reticle and wafer are scanned during scanning exposure in a direction (Y-direction) parallel with the Y-axis, two measuring laser beams 53Y1, 53Y2 or 56Y1, 56Y2 are incident upon a corresponding one of the Y-axis mirrors 52Y, 55Y of the scanning direction. Also, one measuring laser beam 53X or 56X is incident upon the corresponding X-axis mirror 52X, 55X for the non-scanning direction, so that the position (Y-coordinate) of the stage in the scanning direction is measured by the corresponding two-axis laser interferometric system. The position (X-coordinate) of the stage in the non-scanning direction is measured by the corresponding one-axis laser interferometric system.
In this case, the two-axis laser interferometric system for the scanning direction includes a laser interferometer for measuring yawing. The Y-coordinate in the scanning direction is represented by the average of measurement values of the two-axis laser interferometric system. The angle of rotation of each of the wafer stages 51, on which wafer W rests and on the reticle stage 54 reticle R rests, is measured based on a difference between the Y-coordinates at which the two laser beams are incident upon the corresponding Y-axis mirror. During a scanning exposure operation, the wafer stage 51 and reticle stage 54 are moved in synchronization with each other so that the relationship between the X-coordinate and Y-coordinate of the wafer stage 51 and those of the reticle stage 54 match the projection scale (reduction ratio) of the optical projection system, so that the relative rotation angle of these stages is maintained to a fixed value. Although the optical projection system normally used in the conventional apparatus is adapted to project a reverse image of the reticle pattern on the wafer and thus the wafer stage 51 and reticle stage 54 are scanned in opposite directions, it is assumed, for the sake of simplicity, that a non-reverse image of the reticle pattern is projected and the wafer and reticle stages are both scanned in the Y-direction.
If the reflecting surfaces of the mirrors extend parallel with the X-axis and Y-axis with high degree of accuracy, a scanning exposure operation is performed such that the wafer W on the wafer stage 51 is moved in the Y-direction relative to a slit-like exposure region 58. The reticle R on the reticle stage 54 is then moved in the Y-direction relative to a slit-like illuminated region 57 in synchronization with the movement of the wafer W so that an image of a pattern of the reticle R is transferred onto one of shot areas on the wafer W. The thus exposed shot area SAa has an accurate rectangular shape, as shown in FIG. 10(a3). The shot array formed on the wafer W is in the form of a grid in which the shot areas are arranged along the X-axis and the Y-axis, as shown in FIG. 10(a4).
However, if the mirrors 52X, 52Y are rotated clockwise by an angle xcex8 due to yawing of the wafer stage 51, as shown in FIG. 10(b1), the wafer W is scanned in a direction parallel with the reflecting surface of the mirror 52X (direction that is inclined by the angle xcex8 with respect to the original Y-axis), as indicated by the arrow 60b. The stepping of the wafer W in the non-scanning direction is conducted in a direction parallel with the reflecting surface of the mirror 52Y, as indicated by the arrow 61b. In this case, the rotation of the wafer stage 51 is detected based on the inclination of the mirror 52Y. The reticle stage 54 is also rotated by the angle xcex8 in accordance with the rotation of the wafer stage 51, whereby the reticle R is scanned in the rotated direction, as indicated by the arrow 59b, as shown in FIG. 10(b2), while it is being rotated through angle xcex8. Accordingly, the shot area (on which the pattern image of the reticle R is transferred) exposed on the wafer W in the scanning exposure operation is rotated, but has an accurate rectangular shape, as represented by shot area Sab, as shown in FIG. 10(b3). The shot array (shown in FIG. 10(b4)) formed on the wafer W is also in the form of a grid (which will be called xe2x80x9crectangular gridxe2x80x9d) in which the shot areas are arranged in orthogonal directions.
In the conventional step-and-scan type projection exposure apparatus, as described above, the coordinate positions of the wafer stage and reticle stage are measured by the respective laser interferometric systems. Where the X-axis and Y-axis mirrors of the laser interferometric systems have a good orthogonal relationship with each other the exposed shot area has a rectangular shape, even if the wafer stage is rotated due to yawing and the obtained shot array is in the form of a rectangular grid.
However, if the stage or the mirrors of the laser interferometric systems is/are deformed by heat due to changes in atmospheric temperature or an increase in the temperature caused by irradiation with exposure light, and the orthogonal relationship between these mirrors has deteriorated due to such deformation, the exposed shot area may no longer maintain a rectangular shape and the shot array may no longer have a rectangular grid-like shape. This problem is mainly caused because the position of the stage in the scanning direction is conventionally measured by the two-axis laser interferometric system and the angle of rotation of the stage is calculated based on a difference in the measurement values of the two-axis interferometric system. In the examples of FIG. 10, the laser beams emitted by the laser interferometers for measuring yawing of the wafer and reticle stages are incident upon the mirrors 52Y, 55Y for measuring displacement in the scanning direction.
More specifically, FIG. 10 (c1) depicts the case in which the mirror 52X of the wafer stage for measuring displacement in the non-scanning direction, which is not intended for detecting yawing, is inclined by an angle xcex8. In this case, the wafer W is scanned in a direction parallel with the reflecting surface of the inclined mirror 52X, as indicated by the arrow 60c. However, the reticle R, on reticle stage 54, is scanned in the Y-direction, as shown in FIG. 10(c2), since no change in the angle of rotation of the wafer stage is detected. As a result, the shot area SAc, formed on the wafer W, is in the form of a parallelogram, as shown in FIG. 10(c3), and the shot array is also in the form of a parallelogram, as shown in FIG. 10(c4).
FIG. 10(d1) shows the case in which the mirror 52Y of the wafer stage for measuring displacement in the scanning direction and detecting yawing is inclined by an angle xcex8. In this case, the wafer W is scanned in the Y-direction. However, the reticle R is scanned in a direction that is inclined by the angle xcex8 as indicated by the arrow 59d, as shown in FIG. 10(d2), while it is being rotated by an angle xcex8 with respect to the original Y-axis, since a change in the angle of rotation of the wafer stage is detected. As a result, the shot area SAd formed on the wafer W assumes a shape formed by rotating a parallelogram by 90xc2x0, as shown in FIG. 10(d3), and the shot array also assumes a similar shape, as shown in FIG. 10(d4).
An error in the shot array, as shown in FIG. 10(c4) or (d4), which is a linear error (first-order error), may be substantially corrected at the time of exposure by performing so-called enhanced global alignment (EGA). EGA calculates the shot array by statistic processing and conducting stepping of the wafer stage based on the calculated shot array.
However, the shot area is deformed. For example, in the shot areas SAc, SAd an image formed on the wafer W becomes equivalent to an image that is laterally shifted by approximately Dxc2x7xcex8 in the non-scanning direction during scanning exposure. D represents the Y-direction width of the slit-like exposure region 58 of FIG. 10(a1) and xcex8 (measured in rads) represents the angle of rotation of the mirror, resulting in a deterioration of the image.
Even if the shot region that is deformed, as in the shot area SAc or SAd, is subjected to overlap exposure by a one-time exposure-type apparatus, such as a stepper in a so-called mix-and-match mode, corrections for the thus deformed shot areas cannot be made in the one-time exposure-type apparatus. Thus, the deformed shot area involves a distortion error that results in reduced matching accuracy.
The shape of the exposed shot area is undesirably distorted not only when inclination of a mirror of the laser interferometric system is changed, but also when the mirror is deflected or warped along the scanning direction.
In a conventional method for reducing such deterioration of the image a reference mark plate, on which certain reference marks are formed, is fixed on the wafer stage. Relative rotation angles between the reference marks of the reference mark plate and alignment marks on the reticle are measured periodically (upon replacement of wafers, for example). The angle of rotation of the reticle is then corrected based on the results of the measurements. If an angle formed by the reference mark plate and the running direction of the wafer stage, which is determined by the mirror of the laser interferometer, is changed due to thermal deformation of the wafer stage, the rotation angle of the reticle may not be accurately corrected, thereby causing deformation of the exposed shot area.
Where the EGA type alignment is performed, the positions of the alignment marks (wafer marks) affixed on certain shot areas on the wafer need to be detected by means of an alignment sensor. In order to position each shot area on the wafer with respect to the pattern image of the reticle with high accuracy, based on the results of detection of the alignment sensor, a base line parameter is periodically calculated. The base line parameter is a spacing between a reference point (such as the center of detection) of the alignment sensor and a reference point (such as the center of exposure) of the image transferred on the wafer. The calculation is made using the reference mark plate, and is then stored. The results of the alignment sensor are corrected based on the base line parameter. The periodic measurement of the base line parameter is called an xe2x80x9cinterval base line checkxe2x80x9d. The base line parameter is substantially varied if the angle formed by the reference mark plate and the running direction of the wafer stage that is determined by the mirror of the laser interferometer is changed due to thermal deformation, for example, thus causing an increased overlap error.
Accordingly, there is a need for an improved exposure apparatus and method of operation thereof to overcome the above enumerated problems.
A first object of the present invention is to provide a scanning exposure apparatus that is able to maintain a desired shape of a shot area, exposed on a photosensitive substrate, even when the angle formed by mirrors of interferometric systems for measuring the position of a stage is changed.
A second object of the present invention is to provide a scanning exposure apparatus that is able to maintain a desired shape of a shot area, exposed on a photosensitive substrate, even when the mirror of the interferometric system is deflected or curved.
A third object of the present invention is to provide an exposure method that can prevent distortion of the exposed shot area on the wafer, or form the shot array on the wafer into a rectangular grid-like shape, even if a relative angle between the running direction of the wafer stage and the reference mark plate used for detecting the rotation angle of the reticle is changed.
A fourth object of the present invention is to provide an exposure method in which the baseline parameter of the alignment sensor can be measured with a high accuracy, even if the relative angle between the running direction of the wafer stage and the reference mark plate used for measuring the base line amount is changed.
A fifth object of the present invention is to provide an exposure method in which the relative angle between the running direction of the wafer stage and the reference marks used for measuring the base line amount of the alignment sensor is less likely to be changed, whereby the base line amount can be measured with high accuracy.
With reference to FIG. 1 and according to the first aspect of the present invention, a scanning exposure apparatus is provided. The apparatus has a mask stage 9-11 that moves a mask 12 onto which a pattern to be transferred is formed, and a substrate stage 1-4 that moves a photosensitive substrate 5. The substrate 5 on the substrate stage is scanned in a predetermined scanning direction while the mask is being illuminated by an exposure light. The mask 12 on the mask stage includes at a least one-axis interferometric system 13Y1, 7Y disposed on the side of the substrate for measuring the position of the substrate in the Y-scanning direction, a two-axis interferometric system 13X1, 13X2, 7X disposed on the side of the substrate for measuring the position of the substrate stage in a X-non-scanning direction that is perpendicular to the scanning direction at two points of the substrate stage which are spaced apart in the scanning direction, and a rotation angle correcting means 22D, 44R, 44L for correcting a relative rotation angle of the substrate stage and the mask stage based on measurement values of the two-axis interferometric system.
According to the present invention, the two-axis interferometers 13X1, 13X2 are configured to oppose mirror 7X of the non-scanning direction of the substrate stage for moving the substrate 5, so as to determine the coordinate of the stage in the non-scanning direction, based on the average of measurement values of the two-axis interferometers. At the same time, the yawing amount (angle of rotation) of the substrate stage in the non-scanning direction is obtained by calculating the difference between these measurement values. The mask 12 is rotated based on the yawing amount. The angle of rotation of the mask stage may be also calculated from a difference of the measurement values of a two-axis interferometric system disposed in one of either the scanning or the non-scanning direction.
If the angle of the mirror 7X for detecting the position of the substrate stage in the non-scanning direction is changed, as shown in FIG. 3(c1)-(c4), the substrate 5 and mask 12 are scanned while being inclined at the same angle. Therefore, the shot area SA3, exposed on the substrate 5, experiences a rotation but still retains its rectangular shape. If the angle of mirror 7Y for detecting the position of the substrate stage in the scanning direction is changed, as shown in FIG. 3(d1)-(d4), the substrate 5 and mask 12 are scanned without being inclined and, therefore, the shot area SA4 exposed on the substrate 5 retains its rectangular shape. According to the present invention, the substrate 5 and mask 12 are always scanned in the same direction and the shot area exposed on the substrate 5 maintains a desired or target shape.
Even if the shot area has the desired shape, the shot array is not always in the form of a rectangular grid (in which the shot areas are arranged in orthogonal directions), as shown in FIG. 3(c4) and (d4). For the shot array to take on the form of a rectangular grid-like shape, it is desirable that a one-axis interferometric system 13Y2, 7Y be further disposed on the side of the substrate that cooperates with a one-axis interferometric system 13Y1 , 7Y to measure the position of the substrate stage in the scanning direction. The measurements are taken at two points along the substrate stage spaced in the non-scanning direction. Moving direction correcting means 22A, 22B are provided for correcting the moving direction of the substrate stage. The correction is based on the difference between the measurement values of the two-axis interferometric system 13X1, 13X2, 7X, that measures the position of the substrate stage in the non-scanning direction, and the difference between the measurement values of the two-axis interferometric system 13Y1, 13Y2, 7Y, that measures the position of the substrate stage in the scanning direction.
If the stepping direction of the substrate stage in the non-scanning direction is corrected using the difference between the yawing amount measured in the non-scanning direction and the yawing amount measured in the scanning direction, the shot array takes on a rectangular grid-like shape, as indicated by the dotted line in FIGS. 3(c4) or (d4).
Analysis will now relate to when one of the mirrors 21X, 21Y positioned on one side of the mask stage, as shown in FIG. 4, is inclined and its orthogonal relationship is altered. In this case, there is also a possibility that the exposed shot area does not take on a rectangular shape if the position of the mirror 21Y, for detecting displacement of the mask stage in the scanning direction, is measured by a two-axis interferometric system and the control of angle of rotation of the mask stage is based on the difference between the measurement values of the two-axis interferometric system, as in the conventional case.
FIGS. 4(a2), (b2) and FIGS. 5(a2), (b2), respectively, depict the case where two-axis interferometers are configured to oppose mirror (21Y) in the scanning direction of the mask stage and a one-axis interferometer is disposed to oppose mirror (21X) in the non-scanning direction. FIGS. 4(a1) and (a2) depict the case where the position of the substrate stage, in the non-scanning direction, is measured by a two-axis interferometric system in the same manner as in the scanning exposure apparatus according to the first aspect of the present invention. FIGS. 5(a1) and (a2) depict the case where the position of the substrate stage in the scanning direction is measured by a two-axis interferometric system, as in the conventional case.
In these cases, if the mirror 21Y of the mask stage is inclined by the angle xcex8 with respect to the mask 12, as shown in FIG. 4(a2) and FIG. 5(a2), the mirror 21Y is brought parallel with the substrate stage. Therefore, the mask 12 is scanned in the direction indicated by the arrow 37a, 38a, respectively, while being rotated or inclined with respect to the scanning direction of the substrate 5. Accordingly, the exposed shot area SA5, SA7 takes on the shape of a parallelogram rotated 90xc2x0. If the mirror 21X is inclined by the angle xcex8 with respect to the mask 12, as shown in FIG. 4(b2) or FIG. 5(b2), the mask 12 is scanned with the mirror 21Y being parallel with the substrate stage. Therefore, the scanning direction of the mask 12 is inclined, with respect to the scanning direction of the substrate 5 as indicated by the arrow 37b, 38b, respectively, and the exposed shot area SA6, SA8 has the form of a parallelogram.
To prevent such deformations of the shot area, a scanning exposure apparatus according to the second aspect of the present invention is provided which has a mask stage 9-11 that moves a mask 12 on which a pattern to be transferred is formed. A substrate stage 1-4 moves a photosensitive substrate 5, wherein the substrate on the substrate stage is scanned in a predetermined scanning direction (Y-direction) while the mask 12 is being illuminated by an exposure light. The mask 12, on the mask stage, is scanned in the predetermined scanning direction in synchronization with the scanning of the substrate so that the pattern on mask 12 is successively formed on substrate 5.
The scanning exposure apparatus includes a two-axis interferometric system 13X1, 13X2, 7X disposed along one side of the substrate for measuring a position of the substrate stage, in a non-scanning direction (X-direction) perpendicular to the scanning direction, at two points on the substrate stage, which are spaced apart along the scanning direction. The apparatus also includes a two-axis interferometric system 14X1, 14X2, 21X disposed along one side of the mask for measuring a position of the mask stage, in the non-scanning direction (X-direction) perpendicular to the scanning direction, at two points on the mask stage, which are spaced apart along the scanning direction. The apparatus further includes rotating angle correcting means 22D, 44R, 44L for correcting a relative rotation angle between the substrate stage and the mask stage based on measurement values of the two-axis interferometric system along one side of the substrate, and the two-axis interferometric system on the side of the mask.
In summary, the scanning exposure apparatus according to the first aspect of the present invention corrects the relative rotation angle between the substrate stage and the mask stage based on measurement values of the two-axis interferometric system disposed on the side of the substrate for measuring displacement of the substrate stage in the non-scanning direction, so that the substrate stage and mask stage are moved or scanned in parallel, even if the angle formed by mirrors of the interferometric systems on the side of the substrate is altered. Accordingly, the shot area exposed on the photosensitive substrate can advantageously maintain a desired shape (i.e., a rectangular shape). This results in an avoidance of alteration of an image due to distortion of the shape of the shot area and reduces the matching error between the shot area and the exposure apparatus of the one-time exposure type.
The above exposure apparatus further includes a one-axis interferometric system, disposed on the side of the substrate, for measuring a position of the substrate stage in the scanning direction at two points spaced apart in the non-scanning direction. Also included is moving direction correcting means for correcting the moving direction of the substrate stage, based on the difference between of measurement values of the two-axis interferometric system for measuring the position of the substrate in the non-scanning direction. A difference in the measurement values of the two-axis interferometric system for measuring the position of the substrate in the scanning direction, and the stepping direction of the substrate stage in the non-scanning direction, may be corrected so that the shot array formed on the photosensitive substrate has a rectangular grid-like shape. This will further reduce the matching error.
According to the second aspect of the present invention, the position of mirror 7X in the non-scanning direction of the substrate stage is measured by a two-axis interferometric system, and the position of mirror (21X) in the non-scanning direction of the mask stage is measured by a two-axis interferometric system, as shown in FIG. 7. In this arrangement the yawing amount of the substrate stage is obtained from the difference of the measurement values at two points along the mirror 7X and the angle of rotation of the mask stage is obtained from the difference of the measurement values at two points along the mirror 21X. Accordingly, even if the mirror 21Y, in the scanning direction or the mirror 21X, in the non-scanning direction along one side of the mask stage, is inclined with respect to the mask 12, as shown in FIG. 7(a2) or (b2), the scanning direction of the mask 12 is parallel to the scanning direction of the substrate 5. Thus, the exposed shot area SA13, SA14 has a rectangular shape even if shot rotation occurs.
In summary, the scanning exposure apparatus according to the second aspect of the present invention corrects the relative rotation angle between the substrate stage and the mask stage based on measurement values of the two-axis interferometric system disposed on the side of the substrate, for measuring the position of the substrate stage in the non-scanning direction, and measurement values of the two-axis interferometric system disposed on the side of the mask for measuring the position of the mask stage in the non-scanning direction. In this arrangement the substrate stage and mask stage can be moved in parallel for scanning of the substrate and mask, even if the angle formed by the mirrors of the interferometric systems on the side of the mask is altered. Accordingly, the shot area exposed on the photosensitive substrate can advantageously maintain a desired shape (such as a rectangular shape).
According to the third aspect of the present invention, a scanning exposure apparatus is provided, having a mask stage 9-11, which moves a mask 12, onto which a pattern to be transferred is formed, and a substrate stage 1-4, which moves a photosensitive substrate 5. The substrate 5, on the substrate stage, is scanned in a predetermined scanning direction (Y-direction) while the mask 12 is being illuminated by an exposure light. The mask 12 on the mask stage is scanned in the direction (Y-direction), corresponding to the predetermined scanning direction, in synchronization with the scanning of the substrate so that a pattern on the mask 12 is successively formed on the substrate 5.
The scanning exposure apparatus includes a first two-axis interferometric system 14Y1, 14Y2, 21Y for measuring a position of one of either the substrate stage or the mask stage, in the scanning direction at two points that are spaced apart in a non-scanning direction perpendicular to the scanning direction. Also included is a second two-axis interferometric system 14X1, 14X2, 21X, for measuring a position of one of either the substrate stage or the mask stage in the non-scanning direction at two points that are spaced apart in the scanning direction, a mirror deflection amount calculating means 22A for detecting an angle of rotation of the corresponding substrate stage or mask stage based on a difference of measurement values of the first two-axis interferometric system, and for calculating an amount of deflection of a mirror 21X for the second two-axis interferometric system based on the detected angle of rotation and a difference of measurement values of the second two-axis interferometric system.
According to the third aspect of the invention, when the two-axis interferometric system 14Y1, 14Y2, 21Y is disposed for measuring the position of the mask stage in the scanning direction and the two-axis interferometric system 14X1, 14X2, 21X is disposed for measuring the position of the mask stage in the non-scanning direction, the mask 12 is scanned along a curve if the mirror 21X, of the interferometric system for the non-scanning direction is deflected or warped, as shown in FIG. 9. This may cause distortion of the exposed shot area. In view of this problem, a difference of the measurement values of the two-axis interferometric system for the scanning direction is maintained at a fixed value when the mask stage is moved in the scanning direction, so as to prevent the occurrence of yawing of the mask stage. In this state, a difference in the measurement values of the two-axis interferometric system, for the non-scanning direction, is monitored so as to measure the curved shape or deflection of the mirror 21X, for the non-scanning direction. In actual scanning exposure operations, the measurement values of the two-axis interferometric system are corrected by the thus measured amount of deflection of the mirror 21X, so that the mask stage can be linearly moved in the scanning direction and a shot area approaching that of a rectangular shape is exposed.
In a preferred embodiment, the scanning exposure apparatus of the present invention further includes measuring means 6, 19, 20 for measuring a positional relationship between the mask 12 and the substrate stage when a difference in measurement values of a two-axis interferometric system for measuring the position of one of the substrate stage and the mask stage, in a non-scanning direction perpendicular to the scanning direction, exceeds a predetermined threshold value. If the difference in the measurement values of the two-axis interferometric system exceeds the predetermined threshold value, it is probably because the angle of inclination of the mirror for the interferometric system is altered due to thermal deformation. Since the positional relationship between the mask 12 and the substrate 5 can be corrected by re-measuring the positional relationship between them, an error in the shape of the exposed shot area can be reduced. Therefore, the amount of deflection of the mirror can also be measured again, since the deflection amount of the mirror is also capable of being altered.
In summary, the scanning exposure apparatus according to the third aspect of the present invention detects the angle of rotation of one of the substrate stage or mask stage based on a difference of the measurement values of the first two-axis interferometric system for the relevant stage. The amount of deflection of a mirror for the second two-axis interferometric system is calculated based on the detected angle of rotation and a difference of the measurement values of the second two-axis interferometric system. Thus, the deflection amount of the mirror can be accurately detected even upon the occurrence of yawing in the one stage case. In the actual scanning exposure operation, therefore, the stage can be moved in a desired direction for accurate scanning with the deflection amount of the mirror being corrected or canceled. The shot area exposed on the photosensitive substrate can advantageously maintain a desired shape.
The above scanning exposure apparatus further includes measuring means for measuring the positional relationship between the mask and the substrate stage. When a difference of the measurement values of the two-axis interferometric system, for measuring the position of one of the substrate stages and the mask stages in a non-scanning direction perpendicular to the scanning direction, exceeds a predetermined threshold value an error or errors in the shape of a shot area on the photosensitive substrate is advantageously reduced.
The fourth aspect of the present invention, as depicted in FIGS. 10, 11, 13, and 14, provides scanning exposure method for sequentially transferring a pattern on a mask 12 onto each shot area on a photosensitive substrate 5, by scanning the mask 12 and the substrate 5 in synchronization with each other in their corresponding scanning directions while a part of the pattern on the mask 12 illuminated by an exposure light is projected on the substrate on a substrate stage 1-4. A plurality of measurement marks 29A, 29D are formed on the mask 12 along the scanning direction thereof, and a reference mark member 6 on which a plurality of reference marks 35A, 35D are formed, is disposed on the substrate stage, the reference marks having substantially the same positional relationship with the plurality of measurement marks. The exposure method includes a first step of successively measuring a positional deviation of each of the plurality of measurement marks 29A on the mask 12 from a corresponding one of the plurality of reference marks 35A, 35D on the reference mark member while moving the substrate stage in the scanning direction thereof, and detecting a relative rotation angle xcex81 between a direction of an array of the plurality of reference marks 35A, 35D and a running direction of the substrate stage, based on results of the measurement. A second step of the method is successively measuring a positional deviation of each of the plurality of measurement marks 29A, 29D on the mask from a corresponding one of the reference marks 35A, 35D on the reference mark member 6 while moving the mask 12 and the substrate 5 in synchronization with each other in the corresponding scanning directions, and detecting a relative rotation angle xcex82 between the scanning direction of the mask 12 and the scanning direction of the substrate stage, based on results of the measurement. A stepping direction of the substrate stage is determined based on information of the relative rotation angle xcex81, and the scanning direction of the mask 12 is determined based on information of the relative rotation angle xcex82.
According to the fourth aspect of the present invention, the relative rotation angle xcex81, detected when the substrate stage is scanned while the mask 12 is fixed, is a relative angle formed between the direction of the array of the reference marks 35A, 35D, i.e., the longitudinal direction of the reference mark plate 6, and the running direction of the substrate stage during scanning exposure. When the substrate stage is being scanned along the reference mark plate 6, the relative rotation angle xcex82 detected when the mask 12 is moved in the corresponding scanning direction in synchronization with the substrate stage there is a rotation error observed in the scanning directions of the substrate and mask stages. Even if the angle between the substrate stage, and the reference mark member 6 is altered due to thermal deformation of the stage the substrate stage is stepped from one shot area to the next in the direction of the array of the reference marks on the reference mark member 6, or a direction perpendicular to this direction so that the shot array formed on the substrate 5 has a rectangular grid-like shape. Furthermore, the substrate stage is scanned along the reference mark plate 6 and the mask 12 is scanned along the reference mark plate 6, whereby a rectangular shot area can be formed.
In summary, in the exposure method according to the fourth aspect of the present invention, the stepping direction of the substrate stage is determined depending upon the relative rotation angle xcex81 between the direction in which a plurality of reference marks are arranged on the reference mark plate (longitudinal direction of the reference mark plate) and the running direction of the substrate stage (wafer stage). Therefore, even if the relative angle between the running direction of the substrate stage and the reference mark plate is changed, the shot array on the substrate can be formed into a rectangular grid-like shape. Additionally, since the relative rotation error of the mask is determined depending upon the relative rotation angle xcex82 between the scanning direction of the mask and the scanning direction of the substrate stage, the distortion of the exposed shot area on the substrate may be reduced by correcting this relative rotation error.
A scanning exposure method according to the fifth aspect of the present invention includes the same first and second steps as in the scanning exposure method according to the third aspect of the invention. In this exposure method, an angle of rotation of the mask 12 is corrected based on a difference between the relative rotation angle xcex81 and the relative rotation angle xcex82, the angles being obtained in the first and second steps.
According to the fifth aspect of the present invention, the relative rotation angle xcex82, measured when the mask 12 and substrate 5 are moved in the corresponding scanning directions in synchronization with each other, is represented by xcex94xcex8+xcex81, where xcex94xcex8 represents a relative rotation error of the mask 12 with respect to the reference mark member (6). Namely, the relative rotation error xcex94xcex8 of the mask 12 with respect to the reference mark member 6 is represented by xcex82-xcex81. Even when the angle between the substrate stage and the reference mark member 6 is changed due to thermal deformation of the stage, the relative rotation error xcex94xcex8 is measured according to the present invention, and the rotation angle of the mask 12 is corrected by xe2x88x92xcex94xcex8. Thus, the rotation angle of the mask 12 matches the reference mark plate 6. Consequently, the exposed shot area on the substrate 5 has a rectangular shape.
In summary, in the exposure method according to the fifth aspect of the present invention, the angle of rotation of the mask is corrected based on the relative rotation angle xcex81 and the relative rotation angle xcex82. Therefore the distortion of the exposed shot area on the substrate can be reduced even if the relative angle between the running direction of the substrate stage and the reference mark plate is changed.
A scanning exposure method according to the sixth aspect of the present invention includes the same first step as the scanning exposure method according to the fourth aspect of the invention. In the second step of the sixth exposure method, a positional deviation of each of the plurality of measurement marks 35A on the mask 12 from a corresponding one of the plurality of reference marks 29A, 29D on the reference mark member 6 while scanning the mask 12 in the scanning direction is successively measured. A relative rotation angle xcex83 between a direction of an array of the plurality of measurement marks 29A, 29D and a running direction of the mask 12 is detected based on results of the measurement. In a scanning exposure operation, a position of the substrate stage is corrected based on information of the relative rotation angle xcex81, and a position of the mask is corrected based on information of the relative rotation angle xcex83.
According to the sixth aspect of the invention, the relative rotation angle xcex81 detected in the first step is an angle of inclination of the running direction of the substrate stage with respect to the reference mark member 6. The relative rotation angle xcex83 detected in the second step is an angle of inclination of a pattern of the mask 12 with respect to the running, direction of the mask 12. Once the scanning exposure process has begun, the position of the substrate stage is gradually shifted so that the substrate stage is scanned along the reference mark member 6. The scanning direction of the substrate stage becomes parallel with the longitudinal direction of the reference mark member 6, and the position of the mask 12 is gradually shifted so that the mask 12 is scanned along the pattern of the mask 12. This results in a reduction in the distortion of the exposed shot region on the substrate 5.
In summary, in the exposure method according to the sixth aspect of the present invention, the rotation angle xcex83 of the running direction of the mask with respect to the direction of the array of the measurement marks is detected in addition to the relative rotation angle xcex81. The position of the substrate stage during scanning exposure is corrected based on the information of the relative rotation angle xcex81, while the position of the mask during scanning exposure is corrected based on the information of the relative rotation angle xcex83. Accordingly, the distortion of the exposed shot region on the substrate can be reduced even if a relative angle between the running direction of the substrate stage and the reference mark plate is changed.
The seventh aspect of the present invention provides a scanning exposure method for sequentially transferring a pattern on a mask 12 onto each shot area on a photosensitive substrate 5 by scanning the mask 12 and the substrate 5 in synchronization. The sequence involves the transfer in corresponding scanning directions while a part of the pattern on the mask 12, illuminated by exposure light, is projected on the substrate 5, on a substrate stage 1-4, through a optical projection system 8. An off-axis alignment system 34 is provided in the vicinity of the optical projection system 8 for detecting a positioning mark on the substrate. A plurality of measurement marks 29A, 29D are formed on the mask along the scanning direction thereof, while a reference mark member 6, on which first and second reference marks 35A, 37A are formed, is provided on the substrate stage.
The first and second reference marks are spaced apart from each other by a distance corresponding to a spacing between a reference point in an exposure field of the optical projection system 8 and a reference point of the off-axis alignment system 34. The scanning exposure apparatus method includes the steps of moving the mask 12 in the scanning direction thereof while the second reference mark 37A on the reference mark member is observed by the off-axis alignment system 34, and successively measures a positional deviation of each of the plurality of measurement marks 29A, 29D on the mask from the first reference mark 35A on the reference mark member 6. Calculating the spacing (base line parameter) between the reference point in the exposure field of the optical projection system 8 and the reference point of the off-axis type alignment system 34 is then performed. Based on an average value of the positional deviation of each of the plurality of measuring marks 29A, 29D from the first reference mark 35A, a relative rotation error of the mask 12, with respect to the scanning direction thereof, is calculated based on the positional deviation of each measurement mark and a shift of the second reference mark 27A observed by the alignment system.
According to the seventh aspect of the present invention, a positional deviation xcex94B2 of the second reference mark 37A observed by the off-axis alignment system 34 is measured at the same time as the measurement of the relative rotation error xcex83 between the direction in which the measurement marks 29A, 29D are arranged on the mask 12, which is the direction of a transferred image of the mask pattern, and the running direction of the mask 12, based on the reference mark member 6. The base line amount of the alignment system 34 is then calculated based on these measurement values. Thus, the base line parameter can be measured with high accuracy on the basis of the reference mark member 6, even if the angle of the reference mark member 6 relative to the substrate stage is changed due to deformation of the substrate stage.
In summary, in the exposure method according to the seventh aspect of the present invention, the relative rotation error between the direction of the array of the measurement marks on the mask and the running direction of the mask can be measured using the first reference marks on the reference mark member (reference mark plate). Furthermore, since the base line parameter of the alignment system is measured using the first and second reference marks on the reference mark member (reference mark plate), the base line parameter can be measured with a high accuracy even when the relative angle between the running direction of the substrate stage and the reference mark member is changed.
The eighth aspect of the present invention provides a scanning exposure method for sequentially transferring a pattern on a mask 12 onto each shot area on a photosensitive substrate 5. The method includes scanning the mask 12 and the substrate 5 in synchronization in corresponding scanning directions, while a part of the pattern on the mask 12 illuminated by exposure light is projected on the substrate 5, on a substrate stage 1-4, through an optical projection system 8. An off-axis alignment system 34 is provided in the vicinity of the optical projection system 8, for detecting positioning marks on the substrate, and a plurality of measurement marks 29A, 29D are formed on the mask 12 along the scanning direction thereof. A reference mark member 6 is provided on the substrate stage 1-4, the reference mark member 6 having a plurality of first reference marks 35A, 35D corresponding to the plurality of measurement marks on the mask, and a plurality of second reference marks 37A, 37D that are spaced from the respective first reference marks by a distance corresponding to a spacing between a reference point in an exposure field of the optical projection system 8 and a reference point in the alignment system 34. The scanning exposure apparatus method further includes the steps of measuring a positional deviation of one of the plurality of measurement marks 29A, 29D on the mask from a corresponding one of the first reference marks 35A, 35D on the reference mark member 6, and at the same time measuring positional deviations of the second reference marks 37A, 37D by the off-axis alignment system 34. These steps are performed while moving the mask 12 and the substrate 5 in synchronization in the corresponding scanning directions. The first step is repeated with respect to each of the plurality of first reference marks 35A, 35D on the reference mark member 6. A second step of correcting a relative rotation error between the corresponding scanning directions of the mask 12 and the substrate 5, based on the positional deviation obtained with respect to each of the plurality of first and second reference marks is performed. A further step is correcting a relative rotation angle between a direction of an array of the first and second reference marks on the reference mark member 6 and the scanning direction of the substrate stage.
According to the eighth aspect of the present invention, the base line parameter of the off-axis alignment system 34 is measured at the same time as the second step of the exposure method according to the third aspect of the present invention is executed. Based on the results of the measurement, the scanning direction of the substrate stage is corrected on the basis of the reference mark member 6. The scanning direction of the mask 12 is corrected in relation to the corrected scanning direction of the substrate stage. Accordingly, even where the relative angle between the running direction of the substrate stage and the reference mark plate for measuring the rotation angle of the mask 12 and base line parameter of the off-axis alignment system 34 is changed, the distortion of the exposed shot area can be reduced, and the base line parameter of the alignment system 34 can be measured with a high accuracy.
In summary, in the exposure method according to the eighth aspect of the present invention, the relative rotation angle between the corresponding scanning directions of mask and substrate is corrected, and the relative rotation angle between the direction in which the first and second reference marks are arranged on the reference mark member and the scanning direction of the substrate stage is also corrected, based on positional deviations obtained with respect to the respective first and second reference marks on the reference mark member. Accordingly, the distortion of the exposed shot area on the substrate can be advantageously reduced.
The ninth aspect of the present invention provides an exposure method for sequentially transferring a pattern on a mask 12 onto each area on a photosensitive substrate 5. The method involves scanning the mask 12 and the substrate 5 in synchronization in their corresponding scanning directions while a part of the pattern on the mask illuminated by exposure light is projected on the substrate on a substrate stage 1-3, 4A through an optical projection system 8.
An off-axis alignment system 34 is provided in the vicinity of the optical projection system 8, for detecting positioning marks on the substrate 5, and a mirror 41X for measuring a coordinate position is fixed to the substrate stage. At the same time, a plurality of measurement marks 29A, 29D are formed on the mask 12 along the scanning direction thereof, a plurality of first reference marks 35A, 35D corresponding to the plurality of measurement marks on the mask are formed on an upper face of the mirror 41X, and a plurality of second reference marks 37A, 37D are formed with a spacing from the respective first reference marks. The spacing corresponds to a spacing between a reference point in an exposure field of the optical projection system 8 and a reference point of the alignment system 34.
The scanning exposure apparatus method includes the steps of measuring a positional deviation of one of the plurality of measurement marks 29A, 29D on the mask 12 from a corresponding one of the first reference marks 35A, 35D on the mirror 41X. At the same time positional deviations of the second reference marks 37A, 37D are measured by the alignment system 34 while moving the mask 12 and the substrate 5 in synchronization in the corresponding scanning directions. The first step is repeated with respect to each of the plurality of first reference marks 35A, 35D on the mirror 41X. The method further includes a second step of correcting a relative rotation error between the corresponding scanning directions of the mask 12 and the substrate 5, based on the positional deviation obtained with respect to each of the plurality of first and second reference marks, and correcting the spacing (base line amount) between the reference point in the exposure field of the optical projection system 8 and the reference point of the alignment system 34.
According to the ninth aspect of the present invention, upon measurement of the base line parameter, the scanning direction of the mask 12 is corrected based on the first reference marks 35A, 35D on the mirror 41X that also serves as a reference mark plate. Since the mirror (41X) serves both as a mirror for a laser interferometer and the reference mark plate, and the running direction of the substrate stage is parallel to the reflecting surface of the mirror 41X, the angle of inclination of the reference marks with respect to the running direction of the substrate stage is unlikely to change. Accordingly, the base line parameter can be measured with high accuracy and the exposed shot area is less likely to be distorted.
It is to be understood that both the general description above, and the following detailed description are explanatory and are intended to provide further explanation of the invention as claimed.